The current trend in connector design for those connectors utilized in the computer field is to provide both high density and high reliability connectors between various circuit devices. High reliability for such connections is essential due to potential system failure caused by improper connections of devices. Further, to assure effective repair, upgrade, testing and/or replacement of various components, such as connectors, cards, chips, boards, and modules, it is highly desirable that such connections be separable and reconnectable in the final product.
Pin-type connectors soldered into plated through holes or vias are among the most commonly used in the industry today. Pins on the connector body are inserted through plated holes or vias on a printed circuit board and soldered in place using a conventional mechanism. Another connector or a packaged semiconductor device is then inserted and retained by the connector body by mechanical interference or friction. The tin lead alloy solder and associated chemicals used throughout the process of soldering these connectors to the printed circuit board have come under increased scrutiny due to their environmental impact. The plastic housings of these connectors undergo a significant amount of thermal activity during the soldering process, which stresses the component and threatens reliability.
The soldered contacts on the connector body are typically the mechanical support for the device being interfaced by the connector and are subject to fatigue, stress deformation, solder bridging, and co-planarity errors, potentially causing premature failure or loss of continuity. In particular, as the mating connector or semiconductor device is inserted and removed from the connector attached to the printed circuit board, the elastic limit on the contacts soldered to the circuit board may be exceeded causing a loss of continuity. These connectors are typically not reliable for more than a few insertions and removals of devices. These devices also have a relatively long electrical length that can degrade system performance, especially for high frequency or low power components. The pitch or separation between adjacent device leads that can be produced using these connectors is also limited due to the risk of shorting.
Another electrical interconnection method is known as wire bonding, which involves the mechanical or thermal compression of a soft metal wire, such as gold, from one circuit to another. Such bonding, however, does not lend itself readily to high-density connections because of possible wire breakage and accompanying mechanical difficulties in wire handling.
An alternate electrical interconnection technique involves placement of solder balls or the like between respective circuit elements. The solder is reflowed to form the electrical interconnection. While this technique has proven successful in providing high-density interconnections for various structures, this technique does not allow facile separation and subsequent reconnection of the circuit members.
FIGS. 1 and 2 illustrate an LGA socket or connector 20 where first distal end 22 of contact member 24 extends above upper surface 26 of the connector insulator housing 28. As best illustrated in FIG. 2, an LGA device 30 is then pressed against the distal end 22 by applying a load through some mechanical device such as fasteners, springs, heat sinks, or levers. Second distal end 32 of the contact member 24 is electrically coupled to a second circuit member 34, such as a printed circuit board, using a solder ball 36. The connector 20 in FIG. 1 is referred to as “normally open” since the first distal end 22 of the contact member 24 extends above the upper surface 26 prior to engagement with the LGA device 30.
The normally open configuration of the connector 20 illustrated FIGS. 1 and 2 has at least two mechanical features that are undesirable in some circumstances. First, the first distal end 22 of the contact member 24 is exposed to damage prior to being engaged with the LGA device 30. Second, the stress applied to the connector 20 is relatively large due to the relatively large load requirements to be applied to the LGA device 30 in order to maintain reliable long-term contact to the connector 20.